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Method and apparatus for reducing differential mode and common mode reflections in motor drives

a technology of motor drive and differential mode, applied in the field of three-phase ac motor drive, can solve problems such as premature bearing failur

Inactive Publication Date: 2012-05-08
ROCKWELL AUTOMATION TECH
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0015]Generally, the present invention works by providing separate impedance matching for the common mode impedance and differential mode impedance of the power line. In particular, the common mode choke and differential mode choke of the prior art are used to apply the appropriate resistance to the appropriate reflection mode thereby addressing both common mode and differential mode impedance mismatch. For a common type of power cable, the resistor values used for these different impedance matching requirements may be close to each other making it possible to use the same resistor (with an increase in power rating) for the suppression of both common mode and differential mode reflections.
[0037]It is thus an object of one embodiment of the invention to permit the invention to be fabricated from commonly available components that allow for a compact design.

Problems solved by technology

Common mode voltage and current transients can cause premature bearing failure by creating a condition for arcing across the bearings, pitting the finely machined bearing surfaces.

Method used

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  • Method and apparatus for reducing differential mode and common mode reflections in motor drives
  • Method and apparatus for reducing differential mode and common mode reflections in motor drives
  • Method and apparatus for reducing differential mode and common mode reflections in motor drives

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Embodiment Construction

[0048]Referring now to FIG. 6, the conductors 30 of power cable 24 may have an intrinsic inductance represented by discrete inductors 60 distributed in series along the length of each power conductor 30.

[0049]A differential mode impedance will be determined by these inductors 60 together with capacitors 62 passing between each conductor 30 and its neighbor representing the distributed capacitance among the conductors 30, and capacitors 64 passing from each conductor 30 to ground typically presented by a shield around the conductors 30.

[0050]The common mode characteristic impedance of the power cable 24, in contrast, will be determined by inductors 60 together with capacitors 64 passing from each conductor 30 to ground.

[0051]In practice, the differential mode impedance is measured from one end of any conductors 30 to the other two conductors connected to each other at that end and with all three conductors connected to each other at the other end. This differential impedance measurem...

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Abstract

A filter device reduces reflections on power lines from the motor drive to AC motors by providing a differential mode choke in series with a common mode choke both shunted by resistances tailored to the characteristic impedance of the power cable for differential mode and common mode reflections respectively. By treating both common mode based and differential mode based reflections, superior transient control and motor drive performance may be obtained.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS- - -STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT- - -BACKGROUND OF THE INVENTION[0001]The present invention relates to three-phase AC motor drives and particularly to a filter device for power lines communicating between such drives and a connected motor.[0002]Common AC induction motors use three-phase electrical power connected to stator windings of the motor. Each stator winding receives a different conductor of a three-phase power transmission line, where each conductor communicates an AC power waveform shifted with respect to the other conductors by plus and minus 120°.[0003]Referring to FIG. 1, the motor 22 may connect directly to a power grid or, as shown, connect to a solid-state motor drive 10. In this latter case, the motor drive 10 will receive three-phase power 12 from the power grid at a rectifier 14 and the rectifier 14 will convert the received three-phase AC power into DC power on a DC link 16. The rectifier 1...

Claims

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Application Information

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Patent Type & Authority Patents(United States)
IPC IPC(8): H02H3/20H03H5/00H02H9/04
CPCH02H9/005H02M1/126H01F2017/0093H02M2001/123H02M1/123
Inventor TALLAM, RANGARAJAN M.SKIBINSKI, GARY L.
Owner ROCKWELL AUTOMATION TECH
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